Method for making bidirectional iron aluminium alloy magnetic sheet



Oct. 18, 1966 MAMORU NISHIHARA ETI' AL METHOD FOR MAKING BIDIRECTIONAL IRON-ALUMINUM ALLOY MAGNETIC SHEET Filed Deo. 30, 1963 /cc) WUI Pfg. 2

Torque value (/Ofefg/cc) fh /ooo Temperature of the final annealf'ry( 1') Ang/e fram ransverse a'fmc/bn of Me seet United States Patent O Japan Filed Dec. 30, 1963, Ser. No. 334,489 Claims priority, application Japan, Dec. 31, 1962, 38/370 4 Claims. (Cl. 148-112) The present invention relates to a novel method of producing bidirectionally oriented magnetic sheets having a body centered cubic lattice of cubic structure from an iron aluminum alloy material containing 2-6% of aluminum or an iron aluminum silicon alloy material in which less than half of the amount of said 2-6% of aluminum is replaced by silicon.

It is known that, of such kinds of magnetic sheets, a unidirectionally oriented sheet (whose easy magnetization direction corresponds t-o the rolling direction of the magnetic sheet) is superior to a bidirectionally oriented sheet (whose easy magnetization directions are parallel with and normal to the rolling direction of the sheet). It is also known that, from the viewpoint of materials, an iron aluminum all-oy is more advantageous than an iron silicon alloy in obtaining bidirectional properties.

Although a large number of patented inventions regarding method-s of producing bidirectionally oriented magnetic sheets out of iron silicon alloys and 'associated methods of heating or rolling these sheets are already known, it has not thus far been possible to produce truly satisfactory sheets of this type. As to bidirectionally oriented magnetic sheets, their development has not advanced beyond that of m-agnetic sheets of iron silicon alloys, except that the Japanese Patent Publication No. 9,666/58 (applicant: Westinghouse Co., U.S.A.) shows some originality along this line.

This Westinghouse patent discloses a method of producing bidirectionally oriented magnetic sheets by repeatedly cold rolling and annealing the all-oys after having hot rolled them, and by finally finishing the same. According to the method of treatment disclosed therein, however, the degree of preferred crystal orientation would not be always high, although bidirectional properties may be obtained. The degree of preferred crystal orientation determines the electromagnetic properties of a m-agnetic sheet, and it may be said that the higher the degree of preferred crystal orientation, the better the quality of the sheet.

A primary object of the present invention is to provide a sufiicient growth of the nuclei of cubic structure and to increase the degree of preferred orientation of the nuclei of cubic structure in the production of bidirectionally oriented magnetic sheets from iron aluminum alloys.

The iron alloy materials to which `the invention is directed comprise alloys containing 2-6% of aluminum and alloys in which less than half the amount of said 2-6% of aluminum is replaced by silicon. These alloys, in the form of ingots, `are first hot-rolled into thick plates and then subjected to repeated rolling and annealing in order to obtain the desired bidirectionally oriented magnetic sheets.

According to the invention, the thick plates, after having been hot-rolled, are annealed at a temperature above the primary recrystallization temperature of the alloy, whereby the stresses imparted thereto by the rolling process are removed. After annealing, the thick plates are quickly cooled to a Itemperature of G-400 C. and maintained at this temperature for a suitable period of ice time, whereby the carbon dissolved in the plate in a high temperature state at the -time of annealing is allowed to be suitably distributed in the form of carbide within the matrix, thereby contributing to Athe growth of the nuclei of cubic structure during the subsequent operations. After having been subjected to the above operations, the thick pla-tes are subjected to one or more warm rolling operations below 400 C. in order to be reduced to the desired sheet thickness. In the case where warm rolling is performed m-ore than twice, intermediate annealing should be carried out. After having been subjected to the final warm rolling operation, the sheets are then maintained at a temperature of about 500 C. for a suitable period of time, during which time the growth of the nuclei of cubic structure is sufiiciently effected. Finally, in order to improve `the degree of preferred crystal orientation, the sheets are subjected to the final annealing.

The invention is characterized p-articularly by the combination of the warm rolling of thick plates at a temperature of less than 500 C. and the final annealing of the sheets produced by said rolling at a high temperature more than about l050 C. and less than l350 C. By employing this pr-ocess it is possible to economically produce excellent bidirectionally oriented iron aluminum alloy magnetic sheets having a high degree of preferred crystal orientation.

Each of the accompanying drawings (FIGS. 1, 2 and 3) shows the relation between the torque value and the treating conditions.

The invention will concretely be described hereinafter.

The alloy employed in the practice of the prese-nt invention generally contains 2-6% of aluminum and sometimes less than half the amount of said 2-6% of aluminum is replaced by silicon. Carbon and sulfur, which are representative of the inevitable impurity elements of such alloy, are not objectionable so long as they are respectively less than 0.08% and 0.05%. The alloy need not have a particularly high purity. These impurities can be appropriately removed by an :annealing operation in a hydrogen atmosphere during the treating process. In this case, it is not necessary, during preparation for hot rolling, to adjust the carbon content so as to attain a partial presence of the austenite phase at the time of the hot rolling. Other impurities are not objectionable so long as they are as small as possible. The alloy is melted and cast by the conventional method, or any other suitable method, and then is suitably forged or bloomed in order to be formed into .a billet of suitable size which is then hot rolled into a thick plate having a thickness of several millimeters. This thick plate is annealed before it is subjected to the rolling operation. During this annealing, if the carbon content is high, wet hydrogen is preferably and advantageously used so as to effect also decarburization, thereby purifying the material and assisting in obtaining the bidirectional property. This annealing temperature is pref erably selected to be above the primary recrystallation temperature in order to remove the strains caused by the rolling and to dissolve impurities. The crystallization temperature varies according to the composition and reduction ratio of the alloy, but the above-mentioned annealing is usualling carried out at a temperature of more than 700 C. After having been maintained at the annealing temperature for the required period of time, the thick plate is quickly cooled to 200 C.-400 C. and maintained at this temperature, whereby the carbon in the alloy is transformed into carbide which is distributed in the matrix so that the growth of the nuclei of cubic structure at the time of the subsequent annealing is extremely effectively brought about. The temperature and time of this treatment, of course, vary according to the amount of impurities. In some cases, continuous heating and cooling may by employed in the treatment. The annealed blank is subjected to warm rolling at a temperature of G-500 C. Warm rolling provides rolling reduction more easily than cold rolling, and requires lower rolling pressure .for producing a suicient rolling reduction. Needless to say, warm rolling is more advantageous than cold rolling when it is desired to obtain high production rates. The reduction ratio during warm rolling is 60- 90%, and the temperature thereof should be suitably selected to be less than 500 C. That is to say, it should be suitably selected on the basis of the amount of aluminum, which is the principal alloy element, and on the concentration of the other inevitable impurity substances. In the case where warm rolling is carried out more than twice, intermediate annealing should be carried out. diate annealing may be carried out in the same manner as the previously mentioned initial annealing. The alloy sheet, after having been rolled to the desired thickness, is preferably subjected to a heat treatment prior to the final annealing. This heat treatment is carried out by maintaining the alloy sheet at 500 C. or thereabouts for a suitable period of time. This period of time is determined by the amount of impurities. As a result of the heat treatment, the growth of the nuclei of cubic structure is effectively and sufficiently brought about. Following this, the temperature is raised and the final annealing is carried out at a temperature of more than 1050 C. and less than 1350 C. The final annealing is characterized in that it is carried out in the high temperature range inentioned above, whereby the degree of preferred orientation of the nuclei of cubic structure `is greatly imp-roved to such a point that it imparts excellent magnetic properties to the sheet. In particular, this high temperature annealing is extremely effective when used in combination with warm rolling and differs essentially from the previously mentioned Westinghouse method which states that 'a high temperature annealing at 1i100 C. or more will be harmful to the magnetic properties.

The degree of preferred orientation of the nuclei of cubic structure of directionally oriented magnetic sheets can be determined by measuring the torque value of the resulting magnetic sheets with a torque meter.

FIG. 1 is a graph illustrating the variation of the torque value of magnetic sheets produced according to the present invention using various temperatures when rolling the thick plates after initial annealing. As is apparent from this graph, warm rolling at 20G-400 C. is exceedingly favorable to the improvement of the degree of preferred orientation of the nuclei of cubic structure. Cold rolling cannot produce this result. FIG. 2 is another graph illu-strati-ng the effect of the final annealing temperature on the resulting product, it being clearly seen that the final annealing in a high temperature region of more than l050 C. will greatly improve the torque value of the finished sheet (see curve I). It is, however, not until this high temperature annealing is combined with the previously mentioned warm rolling that the high temperature annealing produces the desired effect. For example, those products which have been subjected to cold rolling have extremely low torque values even if their final annealing is carried out at high temperatures, as shown by curve 1I of the FIGURE 2.

The following is an example of a process according to the invention.

In this example, an iron alloy A containing 3.5% of aluminum and another iron alloy B containing 2.6% of aluminum and 0.6% of silicon were used as the starting materials. Firstly, these two kinds of iron alloys were melted and then forged or bloomed into billets. The billets were hot-rolled at a suitable temperature to be formed into thick alloy plates 8.75 millimeters thick. These thick plates were subjected to a decarburization treatment by annealing the same in a wet hydrogen atmosphere at 800 C. for 30 minutes and they were quickly The intermecooled to 300 C. thereby allowing carbide to be distributed. The thick plates, which were maintained at 300 C., were warm rolled at this temperature to be formed into plates 1.75 millimeters thick (reduction ratio being The plates were then subjected intermediate annealing in a wet hydrogen atmosphere at 1000" C. for about 30 minutes, followed by a carbide distributing treatment by quickly cooling the same again to 300 C., and then they were subjected to warm rolling at 300 C., to yield sheets 0.35 millimeter thick, at a reduction ratio of 80%. The sheets were then maintained at 500 C. in a dry hydrogen atmosphere for several hours. Finally, the temperature was raised to l C., at which temperature the final annealing was carried out for 4 hours, whereby bidirectionally oriented magnetic she-ets having a high degree of preferred orientation were produced.

The two types of sheet produced were tested for their magnetic properties, and the torque curves shown in FIG. 3 were obtained. As is apparent from the gure, these products constitute excellent bidirectionally oriented magnetic iron aluminum alloy sheets having a very high degree of preferred orientation of their cubic structure, the peak values of the torque curves reaching to about 1.7 x erg./c.c. and the ratio between the two peak values of the torque curves reaching to about 0.95.

ln the above examples the compositions of the alloys, in percentages, were as follows:

EXAMPLE l (Fe-AI alloy) S 0.007 Cu Ni :Il: Cr Al EXAMPLE 2 (Fe-AZ-Si aZloy) Trace 0.64

0.002 S 0.005 Cu 0.01 Ni 0.01 Cr Trace Al 2.68

It will be understood that the above description of the present invention is susceptible to various changes, modications, and adaptations, and the saine are intended to be comprehended within the meaning and range of equivalents of the appended claims.

What we claim is:

1 A method of producing bidirectionally oriented magnetic'sheets from an iron alloy having 2-6% of aluminum, consisting of the steps of:

(a) initially annealing a hot rolled plate of said alloy in a wet hydrogen atmosphere for 30 minutes at 800 C.;

(b) cooling said plate to 300 C. and maintaining it at that temperature to permit the distribution of carbide therein;

(c) warm rolling said plate at 300 C.;

(d) intermediately annealing said plate at l000 C. for

about 30 minutes;

(e) cooling said plate to 300 C. and maintaining it at that 'temperature to permit the further distribution of carbide therein;

(f) again warm rolling said plate at 300 C. to form a sheet of the desired thickness;

(g) maintaining said sheet at 500 C. in a dry hydrogen atmosphere for several hours to elect the growth therein of nuclei of cubic structure; and

(h) nally annealing said sheet at a high temperature of lO50-l350 C. for a period of four hours.

2. A method of producing bidirectionally oriented magnetic sheets from an alloy having aluminum and silicon present in a total concentration of 2-6%, with the percentage of silicon being less than that of the aluminum, consisting of the steps of:

(a) initially annealing a hot rolled plate of said alloy in a wet hydrogen atmosphere for 30 minutes at 800 C.;

(b) cooling said plate to 300 C. to permit the distribution of carbide therein;

(c) Warm rolling said plate at 300 C.;

(d) intermediately annealing said plate at 1000" C.

for a'bout 30 minutes;

(e) cooling said plate to 300 C. to permit the further distribution of carbide therein;

(f) again warm rolling said plate at 300 C. to form a sheet of the desired thickness;

(g) maintaining said sheet at 500 C. in a dry hydrogen atmosphere for several hours to effect the growth therein of nuclei of cubic structure; and

(h) finally annealing said sheet at a high temperature of l050-l350 C. for a period of four hours.

3. A method of producing bidirectionally oriented magnetic sheets lfrom an iron alloy having 2-6% of aluminum, consisting of the steps of:

(a) initially annealing a hot rolled plate of said alloy in a wet hydrogen atmosphere `for 30 minutes at 800 C.;

(b) cooling said plate to 300 C. and maintaining it at that temperature to permit the distribution of carbide therein;

(c) warm rolling said plate at 300 C. to form a sheet of the desired thickness;

(d) maintaining said sheet at 500 C. in a dry hydrogen atmosphere for several hours to effect the growth therein of nuclei of cubic structure; and

(e) linally annealing said sheet at a high temperature of 1050-1350 C. for a period of four hours.

4. A method of producing bidirectionally oriented magnetic sheets from an alloy having aluminum and silicon present in a total -concentration of 2-6%, with the percentage of silicon being less than that of the aluminum, consisting of the steps of:

(a) initially annealing a hot rolled plate of said alloy in a Wet hydrogen atmosphere for 30 minutes at 800 C.;

(b) cooling said plate to 300 C. and maintaining it at that temperature to permit the distribution of carbide therein;

(c) warm rolling said plate at 300 C. to form a sheet of the desired thickness;

(d) maintaining said sheet at 500 C. in a dry hydrogen atmosphere for several hours to effect the growth therein of nuclei of cubic structure; and

(e) nally annealing said sheet at a high temperature of 1050-1350" C. for a period of four hours.

References Cited by the Examiner UNITED STATES PATENTS 2,046,717 7/1936 Bitter 14S- lll 2,307,391 l/l943 Cole et al. 148--111 3,005,738 10/1961 Pavlovic et al. 14-8-120 3,144,363 8/1964 Aspden et al 14S-31.55 3,147,157 9/1964 Grenoble 14S-l ll 3,164,496 1/1965 Hibbard 148--120 DAVID L. RECK, Primary Examiner.

N. F. MARKVA, Assistant Examiner. 

1. A METHOD OF PRODUCING BIDIRECTIONALLY ORIENTED MAGNETIC SHEETS FROM AN IRON ALLOY HAVING 6% OF ALUMINUM, CONSISTING OF THE STEPS OF: (A) INITIALLY ANNEALING A HOT ROOLED PLATE OF SAID ALLOY IN A WET HYDROGEN ATMOSPHERE FOR 30 MINUTES AT 800*C.; (B) COOLING SAID PLATE TO 300*C. AND MAINTAINING IT AT THAT TEMPERATURE TO PERMIT THE DISTRIBUTION OF CARBIDE THEREIN: (C) WARM ROLLING SAID PLATE AT 300*C.; (D) INTERMEDIATELY ANNEALING SAID PLATE AT 1000*C. FOR ABOUT 30 MINUTES; (E) COOLING SAID PLATE TO 300*C. AND MAINTAINING IT AT THAT TEMPERATURE TO PERMIT THE FURTHER DISTRIBUTION OF CARBIDE THEREIN; (F) AGAIN WARM ROLLING SAID PLATE AT 300*C. TO FORM A SHEET OF THE DESIRED THICKNESS; (G) MAINTAINING SAID SHEET AT 500*C. IN A DRY HYDROGEN ATMOSPHERE FOR SEVERAL HOURS TO EFFECT THE GROWTH THEREIN OF NUCLEI OF CUBIC STRUCTURE; AND (H) FINALLY ANNEALING SAID SHEET AT A HIGH TEMPERATURE OF 1050-1350*C. FOR A PERIOD OF FOUR HOURS. 